1. Field of the Invention
The present invention relates to a process for the calcination of a catalyst containing phosphorus, molybdenum and oxygen used for the production of an unsaturated acid by gas phase catalytic oxidation of the corresponding unsaturated aldehyde. More particularly, the present invention relates to a process for the calcination of a catalyst containing phosphorus, molybdenum and oxygen used for the production of acrylic acid or methacrylic acid by gas phase catalytic oxidation of acrolein or methacrolein.
2. Description of the Prior Art
Various catalysts have been proposed for the gas phase catalytic oxidation of acrolein or methacrolein. Among them, those containing phosphorus, molybdenum and oxygen have relatively excellent properties. Some of the present inventors proposed a catalyst containing phosphorus, molybdenum and oxygen in the specifications of Japanese Patent Publication Nos. 23013/75 and 23014/75. If such a catalyst is prepared under specific conditions, its activity and selectivity are improved remarkably over other prior art catalysts. However, the catalyst still has insufficient reproducibility of performance from batch to batch. As the scale of production is increased, the scattering of performance becomes higher. Thus, the catalyst has not always been satisfactory from an industrial viewpoint.